Mass flow meters can measure a mass flow rate of a fluid directly and a volume flow rate. For instance, when determining volume, a density and mass meter must use the following equation:{dot over (m)}=Q*ρ  (1)
Where:
{dot over (m)} is the mass flow rate;
Q is the volumetric flow rate; and
ρ is the density.
However, in cases where a highly accurate volume flow measurement or energy flow is needed, a user must install a density meter or specific gravity meter in combination with the mass flow meter.
One problem with the combination of a density or specific gravity meter and a mass flow meter is in order to generate a highly accurate volume flow rate or energy flow output an excessive amount of wiring is involved as shown in FIG. 1.
FIG. 1 shows a prior art flow sensor system 10. The prior art flow sensor system 10 can include a density meter 11 and a mass flow meter 12. The density meter 11 and the mass flow meter 12 are positioned within a flow conduit 5 carrying a process fluid. The density meter 11 may comprise any one of well-known density meters, such as a vibrating element density meter, a hygrometer, an x-ray densitometer, a gamma densitometer, etc. The mass flow meter 12 may comprise any well-known meter that measures a mass flow rate, such as Coriolis meter, thermal mass meter, etc. In the above example and throughout this application the density meter may be substituted with a specific gravity(SG) meter so that energy flow output can be obtained.
The prior art flow sensor system 10 also includes a central processing system 13. As shown, the density meter 11 is in electrical communication with the central processing system 13 via electrical leads 14. Similarly, the mass flow meter 12 is in electrical communication with the central processing system 13 via electrical leads 15. Therefore, each of the meters 11, 12 sends signals to the central processing system 13. The central processing system 13 processes the signals received from the density meter 11 to generate a density measurement. Likewise, the central processing system 13 processes the signals received from the mass flow meter 12 to generate a mass flow rate. The central processing system 13 may subsequently generate a volume flow rate based on the generated density and mass flow rate. The volume flow rate may then be provided to a user or another processing system via leads 16. As an alternative, the central processing system 13 may simply output the individual density and the mass flow rate without calculating a volume flow rate. The customer must then use another processing system to determine the volume flow rate based on the output from the central processing system 13.
The prior art flow system 10 suffers from a number of problems. One problem is due to the increased amount of wiring or signal paths required. While the density meter 11 and the mass flow meter 12 are often located relatively close to one another, the central processing system 13 may be located remotely from the density meter 11 and the mass flow meter 12. Consequently, because each meter 11 and 12 communicates with the central processing system 13 independently, the amount of wiring or number of signal paths is duplicative.
Another problem with the prior art system 10 is that if either the density meter 11 or the mass flow meter 12 needs to be replaced, the central processing system 13 needs to be reprogrammed to receive the new signals from the new meter. Often, the central processing system 13 may be a customer's own equipment and thus, the customer is required to perform the updated programming.
Similarly, many users simply want the volumetric flow rate and do not necessarily need to know the particular density or the mass flow rate. However, in the prior art system 10, the user is only provided signals indicating the density and the mass flow rate and is required to perform the calculation of the volume flow rate independently.
Therefore, there is a need in the art for a system that can provide a volume or energy flow output using a density/SG meter and a mass flow rate meter. Further, there is a need in the art for a system that can reduce or eliminate the required signal paths or wiring, especially between the meters and a central processing system. The embodiments described below overcome these and other problems and an advance in the art is achieved. The embodiments described below provide a volume flow rate system that uses one or both of the density/SG meter and the mass flow rate meter to perform the volume or energy flow calculation. Consequently, only one of the meters needs to be in communication with a central processing system, resulting in a reduction in the number of signal paths and/or reduced wiring. Therefore, the system outputs a volume flow rate and the signal paths and/or wiring required to communicate with the central processing system is reduced or eliminated.